Genetics of adaptive traits in rice (Oryza sativa L.) under aerobic condition
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Date
2018
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AAU, Jorhat
Abstract
An investigation on genetic improvement of rice had been taken up to study the performance of few genotypes, their heterosis and combining ability, character association and nature of gene action under aerobic condition. The experiment was carried out at the experimental field of Sarat Chandra Sinha College of Agriculture, Assam Agricultural University, Dhubri during 2015 and 2016 spanning over four seasons. Evaluation of fifteen rice genotypes comprising ten traditional cultivars and five high yielding varieties both in aerobic and irrigated lowland situations revealed sufficient variability and interaction of the genotypes with the environment.
Combining ability analysis in Line x Tester design involving 10 lines of traditional upland genotypes and 5 testers of HYV, revealed importance of both additive and dominance effects. Three lines (Banglami, Nagina 22 and Tamdao) and three testers (Luit, IR 36 and Gopinath) were identified as good general combiner, while six crosses were identified with specific combining ability (SCA) effect for higher number of characters. Days to anthesis, days to maturity, plant height and height growth rate were found to have significant SCA and heterobeltiosis in favourable direction in higher number of crosses. Four crosses viz. Aus Jaria/ IR 36, Kasalath/IR 36, Dimrow/KMJ-13A-6-1-2 and Tamdao/IR36 recorded heterobeltiosis for maximum number of characters (4 each). Significant correlation was observed among mean, heterobeltiosis and SCA for most of the characters. Genetic parameters estimated in Line x Tester experiment revealed that number of productive tillers, plant height and proline content were highly amenable for improvement, whereas, high genetic variability existed for proline content, root shoot ratio, number of productive tillers and grain yield. Significant correlation with grain yield existed for 3 characters (number of productive tillers, spikelet fertility and chlorophyll content) apart from sufficient inter correlation among various adaptive characters. Path coefficient analysis revealed the highest positive direct effect of root weight (1.65) on grain yield, followed by spikelet fertility (1.43) and plant height (0.92). Harvest index (1.25) through spikelet fertility exerted the highest indirect effect, followed by panicle harvest index (1.07) through spikelet fertility.
Generation mean analysis was carried out in three selected crosses viz. Banglami/Luit, Koimurali/Luit and Guni/Gopinath, involving six generations (P¬1, P2, F1, F2, BC1 and BC2). The individual scaling tests were used to test the adequacy of additive dominance model. The gene effects were estimated using three parameter model (joint scaling test) suggested by Cavalli (1952) and six parameter model suggested by Haymen (1958). The analysis of variance among different generations of different crosses revealed significant variation for most of the characters indicating considerable variability in the material studied. All the characters except height growth rate in cross II, recorded significance for at least one of the four individual scaling tests in all the 3 crosses. Estimation of different gene effects and their interactions revealed significant positive additive effect for plant height and height growth rate in all the three crosses. Preponderance of dominance effect in the expression of height growth rate, spikelet fertility, grain yield, harvest index, root weight and root shoot ratio was evident from the significant positive dominance (h) effect in all the three crosses. With respect to interaction effects, all the characters except height growth rate in cross II, exhibited significant interaction effect for one or more epistatic interactions i.e.[i], [j] or [l] in all the three crosses studied. It is evident that for all the yield and other adaptive traits, additive, dominance and interaction effects were present indicating the complex inheritance of the traits under aerobic condition. On the basis of estimation of various parameters under 3 different sets of experiment over 4 seasons, plant height, shoot weight, number of productive tillers, spikelet fertility, proline content, days to antheis and days to maturity were identified as important adaptive traits to be considered for further improvement of aerobic rice.
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